Whatever the design of the pumps used (reciprocating pumps, rotary pumps or horn effect pumps), good results are obtained when the value of the volumetric ratio of the fluid is very low or even zero, because the fluid then acts as a liquid single-phase fluid. These materials can be used when their operating conditions cause no phenomena likely to allow vaporization of a large part of the gas dissolved in the liquid, or when the value of the volumetric ratio at the pump inlet is at most 0.2. It is known from experience that, above this value, the effectiveness of these devices decreases very quickly.
In order to improve the operation of existing devices, a solution consists in separating the liquid phase from the gas phase prior to pumping, and in processing the phases separately, in distinct compression circuits respectively suited to communicate a compression value to a mainly liquid phase or to a mainly gaseous phase. Separate circuits cannot always be used and often lead to bigger, more expensive and more complex pumping systems.
This is the reason why one has tried to develop pumping devices suited not only to increase the total energy of the multiphase fluid, but also capable of producing a multiphase fluid whose volumetric ratio value at the outlet of the pumping device is below the value thereof prior to pumping.
The prior art describes various blade profiles allowing to obtain this result, notably the claimant's patents FR-2,157,437, FR-2,333,139, FR-2,471,501 and FR-2,665,224, which describe precise blade profiles or a geometry selected for the section of flow of the fluid delimited by two successive blades. In any case, these profiles relate to simple blades comprising a single piece, unlike the blades referred to as "blades of tandem design" which comprise at least two blades within a single group.
The performances of multiphase fluid pumping with "simple" blades can be improved.
The prior art thus describes, for example in the article "Optimization for Rotor Blades of Tandem Design for Axial Flow Compressors" published in the Journal of Engineering for Power, Vol.102, p.369, in April 1980, the use of compression devices comprising blades of tandem design.
However, the teaching of this prior art only relates to the compression of single-phase fluids, i.e. fluids that, at the inlet of the compression device, mainly consist of a single phase, either liquid or gaseous. The geometric characteristics of the blades of tandem design described in this document are particularly well-suited for the compression of a single-phase fluid whose behaviour in compression can nevertheless not be compared to the behaviour of a fluid having several phases, for example fluids with at least one liquid phase and at least one gas phase, and they are therefore not suited for pumping a multiphase fluid.
It has been discovered, which is one object of the present invention, that pumping of a multiphase fluid can be improved by using blades of tandem design or "tandem blades" whose geometric configuration is suited to compress a multiphase fluid comprising at least one liquid phase and at least one vapor or gas phase, the proportions of these two phases being likely to vary with time.
In the description hereafter, the skeleton of a blade is defined as the surface which is equidistant at any point to the lower face of the blade and the upper face of the blades.
Considering the intersection of a blade with a surface of the flowing fluid around this blade, a profile for the blade may be defined from geometrical coordinates of the line of the curvature of the blade and the way it varies of the thickness of the blade along this line.
The following references will be used in the description hereafter:
A.sub.ij : refers to a blade bearing number i in the group of blades j, PA0 a.sub.ij : refers to the leading edge of a blade A.sub.ij, PA0 f.sub.ij : trailing edge of a blade A.sub.ij, PA0 G.sub.j : refers to the group of blades, PA0 C.sub.Tj : total chord of a group of blades corresponding to the chord defined from a blade having a profile equivalent to the profile determined from all of the blades, PA0 C.sub.Fj : chord of the first blade of a group of blades, PA0 C.sub.Rj : chord of the second blade of a group of blades, for groups comprising two blades but that could be increased to a number greater than 2 without departing from the scope of the invention, PA0 h refers to the tangential offset corresponding to the projection of distance (f.sub.ij, a.sub.ij) on the peripheral direction (perpendicular to the rotation axis), PA0 .alpha. is the angle defined on substantially coaxial constant-radius, cylindricals, whose axis is on these surfaces, a is the angle between the peripheral direction (perpendicular to the axis rotation) and the tangent to any point at the curve defined by the previous defined skeleton. PA0 parameter 1: the tangential offset h in relation to the pitch t, expressed in the form of the ratio h/t, where t is the pitch corresponding to the distance between the two trailing edges f.sub.21 and f.sub.22 corresponding to the second blades A.sub.21 and A.sub.22 of each group of blades G.sub.1 and G.sub.2, the value of parameter 1 is in the [0.95; 1.05] range, PA0 parameter 2: the ratio of the axial lap r.sub.j and of the total chord C.sub.Tj corresponding to a group of blades G.sub.j that is in the [0.01; 0.15] value range, PA0 parameter 3: the chord ratio R.sub.Cj =(C.sub.Fj /C.sub.Rj) defined, for a group of blades G.sub.j, by the ratio of the value of the chord C.sub.Fj of the first blade to the value of the chord C.sub.Rj of the second blade for one of the groups of blades, between [0.5; 1.5], PA0 parameter 4: the camber ratio .PHI..sub.j defined by the value of the camber .PHI..sub.Fj of the first blade to the value of the camber .PHI..sub.Rj of the second blade of the same group of blades lies in the [0.10; 1] range. PA0 parameter 1: the tangential offset h in relation to the pitch t, expressed in the form of the ratio h/t, where t is the pitch corresponding to the distance between the two trailing edges f.sub.21 and f.sub.22 corresponding to the second blades A.sub.21 and A.sub.22 of each group of blades G.sub.1 and G.sub.2, the value of parameter 1 is in the [0.60; 0.80] range, PA0 parameter 2: the ratio of the axial lap r.sub.j and of the total chord C.sub.Tj corresponding to a group of blades G.sub.j that is in the [-0.01; 0.05] value range, PA0 parameter 3: the chord ratio R.sub.Cj =(C.sub.Fj /C.sub.Rj) defined, for a group of blades G.sub.j, is by the ratio of the value of the chord C.sub.Fj of the first blade to the value of the chord C.sub.Rj of the second blade for one of the groups of blades, between [0.5; 1.5], PA0 parameter 4: the camber ratio .PHI..sub.j defined by the value of the camber .PHI..sub.Fj of the first blade to the value of the camber .PHI..sub.Rj of the second blade of the same group of blades lies in the [0.10; 1] range. PA0 it allows to minimize the separation of the liquid and gas phases contained in the effluent by favouring at least partially their phase re-mixing, PA0 water power losses are minimized because: PA0 the blades are better suited to the incidence of the flow entering the compression device, PA0 the deceleration rate of the fluid, which is high in case of great blade cambers and notably leads to an increase in water losses and flow separation risks, is minimized thereby, and PA0 at the level of the stator, the tandem design of the blades improves fluid guidance and thus allows the velocities of the fluid trickles to be evened out in the outlet section.